Mmm, not harem in the 4 vols of the manga I've poked. There are rivals though. And I guess love triangles?
Spoiler for zomg boytoys and other junk:
Takeshita/Yamada's best friend has a boyfriend that's 2 yrs older than her.
The girl with glasses, Miyano Mayu?, has a crush on Kosuda iirc. osananajimi (ry
And a girl we'll see later later on, Kanejou Kyouka, voiced by Kobayashi Yu....... Uh, she's Yamada's rival in the sense that she's pretty and popular. iirc, Yamada still wins the popularity contest in their grade/class. The real funny thing is she has a crush on her older brother, I think. ffs, I can't really read Chinese scans. Need to get the original Japanese. >_>;
rite, rite, love triangles.
Kanejou Kyouka → Kanejou Kei'ichi the older bro who also proposed to Yamada → Yamada → Kosuda ← Miyano Mayu
.... Not really a triangle, but I hope you get the idea.
Also, Yamada's younger sister ftw.